Anhydrous halide complexes are key starting materials in the synthesis of transition metal, lanthanide and actinide complexes. For non-aqueous thorium chemistry, ThBr4(THF)4 and ThCl4 have been the most commonly used precursors, but their syntheses suffer from several inconvenient drawbacks, which have, in turn, greatly hampered progress in thorium research. For example, the synthesis of ThBr4(THF)4 requires thorium(0) metal, a material which is both expensive and available at only a small number of institutions. Furthermore, synthesis of thorium(0) metal is highly dependent on the type of thorium metal used (e.g., turnings, powder or chips) and the complex is thermally sensitive with ring-opening and subsequent polymerization of THF being a problem. The synthetic procedures for ThCl4 require special equipment and more dangerous protocols that involve elevated temperatures (300-500° C.). For example, one method involves reacting thorium dioxide or thoria (ThO2) with CCl4 vapor at 450-500° C. for several days, while another requires heating thorium metal with NH4Cl at 300° C. for 30 h to initially generate (NH4)2ThCl6, which is then heated at 350° C. under high vacuum to ultimately give ThCl4.
The increasing use of thorium in catalysis and materials science, coupled with the growing interest in developing a proliferation-resistant thorium nuclear fuel cycle, creates a need for straightforward access to anhydrous thorium(IV) starting materials.